Transcript Where do stars come from?

Stellar Evolution
Forces build inside the protostar until they are
great enough to fuse hydrogen atoms together
into helium.
In this conversion a tiny amount of mass is
turned into a large amount of energy.
For a star of the Sun’s size, 5 million tonnes start
to be converted into energy every second. The
protostar detonates into a star.
Gravity
Pressure
of fusion
Pressure
of fusion
Pressure
of fusion
Pressure
of fusion
Gravity
Gravity
Gravity
https://www.youtube.com/watch?v=mzE7VZMT1z8
Orbits of
Mars
Earth
The Sun as a Red Giant in
5,000,000,000 years time
300 million km
Dormant
hydrogen
fusing shell
Carbonoxygen
core
Heliumfusing shell
7. With no fusion energy to keep the
core inflated, it collapses for one last
time. The carbon is crushed into a
diamond the size of the Earth.
8. The outer layers of the Red Giant
are shed into space as giant gas and
dust shells. They are illuminated by
the remaining tiny White Dwarf star.
Astronomers thought these
dim clouds looked a bit like
planets so they called them
Planetary Nebula.
Bellatrix
Example: The blue giant star Bellatrix, in the
constellation Orion, is coming to the end of its
hydrogen fuel
Betelgeuse
Betelgeuse dwarfs most other stars
4. Eventually the star creates a core of iron
700 million km
3. When a Red
Super Giant runs out
of Helium fuel it has
enough heat and
pressure in its core
to fuse Oxygen and
Carbon to make
even bigger atoms
Iron core
Silicon
Neon
Oxygen
Carbon
Helium
Hydrogen
The core of the red giant becomes an onion-like structure
with an iron core.
5. As the fuel runs out, the core shrinks and gets hot enough
to fuse iron.
( REMEMBER: As the star fused hydrogen, helium, carbon and
oxygen it created enough energy to keep itself supported
against the crushing force of gravity.)
6. Unlike the fusion of smaller atoms, when iron fuses it
SUCKS IN energy. The giant star is millions of years old but it
now collapses in seconds.
7. Billions of tons of star material hurtle into the core and
then bounce back out in the biggest explosion in the Universe
– A Supernova.
8. What remains from the explosion depends on the size
of the original star
1.5 – 3 solar masses: form one giant, 12 mile diameter atomic nucleus
composed only of neutrons (all of the protons and electrons have been
squeezed together to form neutrons).
• This is a neutron star. The force of its tremendous gravity is balanced
by the repulsion of the neutrons.
3+ solar masses: and there is no force greater than the star’s gravity.
• The star collapse never stops, it disappears leaving only its mass to
create a gravity field.
• Nothing goes fast enough to escape, not even light. This is a black
hole.
The gravity near to a black hole is so strong that even
light does not go fast enough to get away
Singularity – all the mass is
squeezed into a point
Event Horizon – the outer
edge where the force of
gravity is great enough to stop
light escaping. The event
horizon of the smallest black
holes created by supernovae
should be about 12km across.
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